Process for the manufacture of glycolic acid.



i No Drawing 7 NIT D STATES OTTO LIEBKNECHT, OF FRANKFORT-ON-THE-MAIN, 'GERMAIVY, ASSIGNOR TO ROESSLER 8a HASSLACHER CHEMICAL 00., OF NEW YORK, N. Y., A CORPORATION OF NEW I YORK.

PROCESS FOR THE MANUFACTURE OF GLY COLIC ACID.

To all whom it may concern:

Be it known that I, Orro LIEBKNncHT, a subject-of the German Emperor, and a resi dent of Frankfort-on-the-Main, Germany, have invented a certain new and useful Improvement in Processes for'the Manufacture of Glycolic Acid, of which the following is a specification.

This invention relates to a more economical and effective process of-manufacturing glycolic acid by the electrolytic reduction of oxalic acid than heretofore.

I- have described a process for the manufacture ofglycolic acid by the electrolytic reduction of oxalic acid in my. United States Patent No. 837,083 patented November 27 1906, in which process there is a cathodic overvoltage and the conduction of the cur-- rent is through a suitable inorganic acid, such as dilute sulfuricor hydrochloric acid, rather than through the-oxalic acid. In my patented process the oxalic acid to be electrolytically reduced is concentrated to a certain degree'and I have found, in practicing the same, that it is easy to carry the degree of concentration too far whereby the oxalic acid is caused to participate in the conduction of the current and to go to the anode Where it is oxidized into carbonic acid.

I have discovered by experiment and re: search that the slow addition of solid or dissolved oxalic acid to the catholyte during the electrolysis, so that oxalic acid is always present for reduction by the hydrogen developed at the cathode, permits a much higher concentration of glycolic acid than heretofore, that isup to 40% and more, re-

- sulting in a much more favorable and economical method of making glycolic acid because of working with such higher concentration. In such casethere is no fear of going too far in cathodic reduction and anodic decomposition of the oxalic acid by oxidation and an .ilmost voluntary progressive enrichment of the catholyte in glycolic acid is obtained. An explanation of this surprising fact, quite contrary to the communications in the literature (see Claus Annals B. 145 p. 256), lies in the circumstance that the glycolic acid, even at the higher degree of concentration, is not further reduced to acetic acid and, as a mono-basic and much weaker acid, ofiers more resistance to the electric current. I have further discovered that the conversion of oxalic acid into gly- Specification of Letters Patent.

Patented Jan. 2,1912.

Application filed March 1, 1911. Serial No. 611,586.

colic acid can be carried out in a uicker and more favorable manner, by starting with a considerably concentrated solution of oxalic acid, (20 to 30% and more), the current density at the same time being proportionally increased from 250 to about 500 amperes per square meter of cathode surface and higher. This results in the unforeseen circumstance that the concentration of the inorganic acid employed may be decreased to lessthan 10% and even to 2 or 3%, or the acid may be omitted entirely, without the fear of the anodic oxidation going too far. This is particularly true if it be arranged so that the level of the liquid in the anode compartment is higher than the level of the liquid in the cathode compartment, for this will prevent the oxalic acid from entering the anode compartment In this manner solutions of glycolic acid may be obtained up to a concentration of 40% and more with but 3% or less} of inorganic or mineral acid. Particularly favorable results are obtained by the use of cathodes having a large effective surface, such as those used in accumulators of the Plant plate type.

As an example of one way of carrying out my new process I give the following: Twenty-five parts by weight of crystallized oxalic acid are dissolved in about eighty parts by weight of water to which is added seven parts by weight of a suitable inorganic or mineral acid, sulfuric acid of a specific gravity of 1.6 having been found satisfactory. This solution forms the catholyte, which should be placed in the cathodic compartment of a suitably electrolytic apparatus provided with a suitable diaphragm. The

cathodes should preferably. be in the form of accumulator electrodes as above described. The anolyte comprises a twenty five to thirty per cent. sulfuric acid'for example, as such gives a good conductivity. The density of the current at the cathode in the example given should be from five hundred to six hundred amperes per square meter of cathode surface. When the larger part of the oxalic acid has been converted into glycolic acid, which fact is ascertained by test, solid or dissolved oxalic acid is slowly added to the catholyte to bring the same up to the degree of concentration of oxalic acid desired. This operation is repeated until the solution contains glycolic acid in the desired degree of concentration. Of course portions of the catholyte could be removed from time to time, enriched with oxalic acid and returned to the cathode chamber instead of introducing the oxalic acid directly into the cathode chamber. I have found that by thus slowly adding seventy five parts by weight of crystallized oxalic acid to the above solution, a solution is finally obtained which contains but little mineral acid and over forty grams of glycolic acid in each one hundred grams of catholyte. The concentration may easily be carried to a still greater degree if desired.

'As above stated the amount of mineral acid may be decreased especially if the anolyte stands at a higher level than the catholyte. The oxalic acid may be added continuously if desired rather than intermittently. Hydrochloric acid may be substituted for sulfuric acid if desired. I refer to my Patent No. 837,083 for other details common to the two processes.

As it is obvious that the process herein described may 'be practiced in a number of different ways with considerable variation, I do not restrict myself to the steps or proportions described further than the scope of the claims demand but What I claim and desire to secure by Letters Patent of the United States is:

l. A process for the manufacture of glycolic acid from oxalic acid, consisting in the electrolytic reduction of oxalic acid in solution in the cathode compartment of an electrolytic apparatus in the presence of electrodes having a cathodic overvoltage, while maintaining the quantity ofoxalic acid in the solution at such a point that it is always present for reduction by the hydrogen developed at the cathode.

2. A process for the manufacture of Q glycolic acid from oxalic acid, consisting in the electrolytic reduction of oxalic acid in a solution of a suitable inorganic acid in the cathode compartment of an electrolytic apparatus in the presence of electrodes having a cathodic overvoltage, while maintaining the quantity of oxalic acid in the-solution at such a'point that it is always present for reduction by the hydrogen developed at the cathode.

3. A process for the manufacture of glycolic acid from oxalic acid, consisting in electrolytic apparatus by a current having a density of over approximately 250 amperes per square meter of cathode surface, the initial concentration of the oxalic acid solution being increased proportionally to the increase of current density.

5. A -process for the manufacture of glycolic acid' from oxalic acid, consisting in the elctrolytic reduction of oxalic acid dissolved in a suitable dilute inorganic acid of less than 10% concentration in the cathode compartment of an electrolytic apparatus, by a current having a density of over approximately 250 amperes per square meter of cathode surface, the initial concentration of the oxalic acid solution being increased proportionally to the incr easej ofv current density.

6. A process for the manufacture of glycolic acid from oxalic acid, consisting in the electrolytic reduction of oxalic acid in solution in the cathode compartment of an electrolytic apparatus by a current having a density of over approximately 250 amperes per square meter of cathode surface, the initial concentration of the oxalic acid solution being increased proportionally to the increase of current density and maintaining the anolyte at a higher level than.

the catholyte.

7. A process for the manufacture of glycollc acid from oxalic ac1'd, ':consisting.

in the elctrolytic reduction of oxalic acid in solution in the cathode compartment of an electrolytic apparatus in the presence of accumulator electrodes having aicathodic overvolt-age, while maintaining the quantity of oxalic acid in the solution atsuch a po nt that it is always present for reduction by the hydrogen developed'ntthe cathode.

8. A process for the manufacture of glycolic'acid from oxalic acid, consisting in the electrolytic reduction of oxalic-acid in solution in the cathode compartment of an electrolytic apparatus by a" current having a density of over approximately 250 amperes per square meter of cathode surfacc, the initial concentration of the oxalic acid solution'being increased proportionally to the increase of current densityland the quantity of oxalic acid in the' sfoliie on1beingmaintained at such a point thatf; it is always present for reduction by the hydrogen developed at the cathode.

In testimony whereofLha've signed my name to this specification in the presence of two subscribing witnesses.-

OTTO LIEBKNECHT. 

